Lacrimal fluid covers eye ball surface consisting of cornea and conjunctiva to maintain wettability of cornea and conjunctiva, and prevents drying. In recent years, however, an increasing number of people report various symptoms including feeling of fatigue and foreign sensation, namely, dry eye syndromes, which are caused by dry surface of cornea and conjunctiva due to lacrimal fluid decrease, dryness of eye during wearing contact lenses, or dryness of eye during operation of OA equipment and the like. Dry eye sometimes accompanies corneal epithelial disorder, corneal epithelial erosion and the like due to disorders of corneal epithelial cells. In a serious case, corneal ulceration and eye infection may be developed. To mitigate such various conditions caused by drying, artificial lacrimal fluids containing salts such as sodium chloride and the like as a main ingredient, eye drops containing hydroxyethylcellulose, chondroitin sulfate or hyaluronic acid and the like have been used. As the situation stands, however, there is no satisfactory agent as yet.
Lacrimal fluid is said to show pseudoplasticity. That is, the viscosity of lacrimal fluid decreases when a force is applied by blinking, and increases when the force is not applied. Therefore, lacrimal fluid has unique property in that it has low viscosity and becomes thin during blinking to facilitate blinking, but it becomes highly viscose before and after blinking to cover the eye surface for protection. As a polymer compound showing such pseudoplasticity, xanthan gum is known.
As an ophthalmic composition containing xanthan gum, the following have been reported. For example, an ophthalmic composition containing echothiopate iodide and xanthan gum is disclosed, and xanthan gum has been reported to enhance the treatment effect of echothiopate iodide (U.S. Pat. No. 4,136,177). In addition, an ophthalmic composition containing xanthan gum and a carbonate dehydratase inhibitor has been disclosed, where xanthan gum is used to improve ophthalmic bioavailability of the carbonate dehydratase inhibitor (JP-T-2001-508035, JP-T-2002-501017, JP-T-2002-506461). For the purpose of improving ophthalmic bioavailability of a drug, xanthan gum is used, and an ophthalmic composition containing a carbonate dehydratase inhibitor, a prostaglandin derivative and xanthan gum has been disclosed (JP-T-2002-501533, JP-T-2002-521332, JP-T-2002-521333). An ophthalmic composition containing quaternary nitrogen-containing ethoxylated glycoside and xanthan gum has been disclosed for the treatment of dry eye (JP-T-2001-516713). In addition, an ophthalmic composition containing xanthan gum, which is gelated upon contact with the eye, has been disclosed (JP-T-2002-510654).
However, no report is found on an ophthalmic composition containing xanthan gum and an amino acid. Moreover, it is not known that xanthan gum has a corneal epithelial cell protecting action, or corneal epithelial cell protecting action can be improved by combining xanthan gum and an amino acid.